Settle an arguement

[eddieboy]

Can someone please tell me the maximum Zs for a 10A Type C Rcbo to BS En 61009-1?

 

[Guest123]

Technically, as there is the additional 30mA RCD element present, the maximum Zs would be 1667 ohms.

 

[ackbarthestar]

Can someone please tell me the maximum Zs for a 10A Type C Rcbo to BS En 61009-1?

Lol,

The MCB part of it from 41.3 gives 2.3 Ohms
The RCD part of it from 41.5 gives 1.67k Ohms, which translates into 200 Ohms

Looks like you're both right

However, .............. we always look at a R1 + R2 + the Suppliers Ze for a TN system which would satisfy the disconnection times in 41.1

 

[telectrix]

correct lenny, but ignoring the rcd bit it would be 2.3

 

[telectrix]

Lol,

The MCB part of it from 41.3 gives 2.3 Ohms
The RCD part of it from 41.5 gives 1.67k Ohms, which translates into 200 Ohms

Looks like you're both right

However, .............. we always look at a R1 + R2 + the Suppliers Ze for a TN system which would satisfy the disconnection times in 41.1

where's 200 ohms come from?

 

[Guitarist]

where's 200 ohms come from?

I think he means the part which says that 1667 is the minimum figure, followed by the part that says it should "really be no higher than 200 ohms"

 

[eddieboy]

Thanks for the replies guys. I was under the impression table 41.5 was for a TT system and 41.3 for a TN system.

 

[ackbarthestar]

where did 200 Ohms come from?

It is a composting anomaly - all it needs is a bit of ground work !

 

[Deleted member 9648]

Thanks for the replies guys. I was under the impression table 41.5 was for a TT system and 41.3 for a TN system.

see 411.4.9

 

[jamie-spark]

if max zs = 1667 we are still limited by the l-n impedance of the circuit where a 5s disconection time is required

 

[Deleted member 9648]

if max zs = 1667 we are still limited by the l-n impedance of the circuit where a 5s disconection time is required

See 435.1

 

[jamie-spark]

heres my reasoning

when a circuit is protected by an rcd, the rcd will trip in the event of a fault between line conductor and protective conductor.the rcd will not operate in the event of a fault between live conductors, including line to neutral.

if the line to neutral loop impedance exceeds the values given in tables 41.3 & 41.4 the overcurrent device will not trip in the ggiven times that is 5s or instantaneously for circuit breakers. BS 7671 allows this situation in reg 435.1,providing overload protection is given by the overcurrent device and the abiatic equaution of 434.5.2is met
.
for simplicity designers will probably wish for the operation of the overcurrent device in the times of tables 41.3 & 41.4 in which case lengths need to be limited as follows----------

 

[Guest55]

where's 200 ohms come from?

On site guide , bottom of page 11 ,

Quote
"The resistance of the consumers earth electrode should be as low as possible and a value exceeding 200 ohms may not be stable."

 

[JUD]

Here's a tip for future reference....

For type B breakers, max Zs = 46 ÷ In
For type C breakers, max Zs = 23 ÷ In
For type D breakers, max Zs = 11.5 ÷ In

Remembering this will save looking in the books all the time :coolgleamA:

 

[jamie-spark]

that quote was from the iet electrcians design guide